When it rains, it’s time to shoot film camera. When bright daylight, either digital or film, you get a beautiful color rather easily. However, when it rains, it’s hard to get a vibrant color with a digital camera. You might get grayish color. It might be far from what you’ve desired.
If you shoot a film camera with a Kodak Portra 400 film loaded, rain won’t be of your concern. On top of this, you can use lights from buildings to make a beautiful bokeh in the rain just like the photo below. ISO 400 might be tough to shoot at late evening where you see lights from buildings, but when it rains during a daytime, ISO 400 gives you fast enough shutter speed.
Most importantly, rain from the ground (it works best with rock-based streets) provides reflections. Reflections in combination with one stop overexposed film shot make a beautiful color.
The only disadvantage is that your camera would get wet. Especially Leica M as far as I know, it’s not weather-sealed gear. So oftentimes, I hold an umbrella until I am ready to shoot. As soon as I take a shot, I use the umbrella again to protect my gear.
This summer, why don’t you take some shots with film when it rains!